MEDIUM: 51d: add support for 51Degrees V4 with Hash algorithm

MEDIUM: 51d: add support for 51Degrees V4 with Hash algorithm

This patch also adds a set of new global options:

- 51degrees-use-performance-graph { on | off }
- 51degrees-use-predictive-graph { on | off }
- 51degrees-drift <number>
- 51degrees-difference <number>
- 51degrees-allow-unmatched { on | off }

To build using the latest 51Degrees V4 engine with Hash algorithm, set
USE_51DEGREES_V4=1.

Other supported build options are 51DEGREES_INC, 51DEGREES_LIB and
51DEGREES_SRC which needs to be set to the directory that contains
headers and C files. For example:

make TARGET=<target> USE_51DEGREES_V4=1 51DEGREES_SRC='51D_REPO_PATH'/src